This invention relates to an enclosed type battery and more specifically to a structure of a positive plate used for this battery and a production method of the positive plate.
The positive plate of the enclosed type battery such as a button type battery or a coin type battery is generally produced by solidifying powder of an inorganic compound by molding or the like method. For this reason, the positive plate has essentially the property of allowing the impregnation of a liquid and keeping the liquid. On the other hand, it is a recent trend to increase the density of the positive plate as highly as possible in order to increase the energy density (wh/g, wh/ml). Accordingly, voids of the positive plate are reduced and it becomes difficult to impregnate the positive plate with an electrolyte.
U.S. Pat. No. 4,060,668 solves this problem by forming a material of the positive plate by an aggregate of porous semi-rigid particles having the composition consisting of about 40 to 99% by weight of carbon black, at least 1% by weight of a mechanical binder, which is inert inside the battery to be used, and the balance of graphite so that a number of liquid paths are formed between adjacent particles to allow the electrolyte to sufficiently diffuse into the positive plate material during the service life of the battery. However, this method involves the problem in that since the density of the positive plate is reduced, the energy density is also reduced accordingly.